Single spin process for blood plasma separation and plasma composition including preservative

ABSTRACT

A screening method for the identification of a characteristic of a target nucleic acid in a whole blood sample, including positioning a composition comprising whole blood and at least one preservative agent within a centrifuge, centrifugating the composition to isolate a plasma that includes at least one target nucleic acid for further analysis and analyzing the at least one target nucleic acid to identify a characteristic about the at least one target nucleic acid, and a composition including the plasma, the preservative agent, and any other ingredient, which is produced by the method.

TECHNICAL FIELD

The teachings relates generally to separation of blood plasma in whole blood for analysis of preserved components.

BACKGROUND

The demonstration by Leon et al. in 1977 that cell-free plasma DNA is elevated in cancer patients paved the way for the present day interest in cell-free plasma nucleic acid in disease diagnosis. More recently, Lo et al. Lancet 350 (1997) 485-487 have identified the existence of circulating cell-free fetal nucleic acids in maternal plasma. Since this work, a number of studies have demonstrated that cell-free fetal nucleic acids present in maternal plasma can be used in non-invasive prenatal diagnosis.

The difficulty in obtaining the genetic material of a fetus has presented a number of barriers to testing for the many known genetic markers for hereditary disease, and for other fetal characteristics.

Also in recent years there have been substantial developments in the isolation of circulating tumor cells and their attendant nucleic acids.

For the above testing, and for other newer forms of analysis, it has become recognized that the processes can be best achieved by isolating matter contained in a whole blood draw, preferably by way of a direct blood draw. Certain products (e.g., Cell-free DNA BCT®, Cell-free RNA BCT® and Cyto-Chex BCT®) have been developed and commercialized to address the surprising recognition that certain reagents can be included in a blood collection tube (e.g., agents in addition to a conventional anti-coagulant). See, e.g., U.S. Pat. Nos. 8,304,187 and 8,586,306 and U.S. Patent Publication Nos. 2010/0184069, 2014/0054508, 2011/0111410, 2004/0137417, 2010/0317107, 2014/0080112 and 2014/0199681, all incorporated by reference for all purposes. The agents are selected and used in certain predetermined amounts so that the desired target matter for analysis is preserved for analysis. Another benefit that can be achieved is the preservation of integrity of target nucleic acids, so that further analysis is made readily possible.

In connection with at least the isolation and testing of fetal nucleic acids within maternal blood, early researchers also recognized that certain sample handling techniques were critical to a successful analysis. In particular, work by a team that included one of the industry's pioneer leaders, Dennis Lo, determined that a two-stage centrifugation protocol was critical to quantification of DNA in maternal plasma. See Chiu, et al., “Effects of Blood-Processing Protocols on Fetal and Total DNA Quantification in Maternal Plasma”, Clinical Chemistry (47:9) 1607-1613 (2001). Under that approach, a sample is centrifuged during a first stage for a first substantial period of time (e.g., about 10 minutes) at a first speed. After the first stage, resulting plasma is removed and subjected to a second stage of centrifugation. The second stage is for a second substantial period of time (e.g., about 10 minutes) at a second speed higher than the first speed, such as by about 10 times. Literature supports that the industry ostensibly has come to accept a two stage centrifugation as a standardized approach. See, e.g., Norton et al., “A New Blood Collection Device Minimizes Cellular DNA Release During Sample Storage and Shipping When Compared to a Standard Device”, Journal of Clinical Laboratory Analysis (27) 305-311 (2013), Chan et al., “Size Distributions of Maternal and Fetal DNA in Maternal Plasma”, Clinical Chemistry (50:1) 88-92 (2004) and Fan et al., “Analysis of the Size Distributions of Fetal and Maternal Cell-Free DNA by Paired-End Sequencing”, Clinical Chemistry (56:8) 1279-1286 (2010), (all incorporated by reference herein for all purposes).

Unfortunately, as can be seen, a process that includes two centrifugations and an intermediate separation step can be tedious, time consuming and potentially difficult to automate. To further increase widespread acceptance of the non-invasive analytical techniques described, it is expected that the industry will need to find ways to assure high quality analysis, while also contributing to a reduction in processing steps that can be a potential source of error.

It would therefore be of great benefit to develop sample processing techniques that would optimize and/or the amount of fetal or other nucleic acids (DNA and/or RNA) recoverable from a whole blood sample while also reducing the time and steps necessary for effective isolation. As a result, the isolation and testing of the nucleic acids may be more reliable and may have improved diagnostic capabilities. It would also be a great benefit if the techniques would employ ingredients that are considered free of any significant amounts (e.g., containing only trace amounts at most) of potentially toxic substances, such as formaldehyde, or other aldehydes.

The present teachings address the need for an efficient and consistent method of preserving and testing nucleic acids from within a plasma separated from a whole blood sample. By providing an improved protocol herein, it is now possible to reproducibly recover nucleic acids (e.g., without limitation, fetal cell free DNA and/or RNA, and/or nucleic acids (e.g., DNA) of circulating tumor matter, mRNA, or other nucleic acid), thereby improving the diagnostic reliability of the nucleic acids, and helping to maintain the structural integrity of the nucleic acids. The present teachings helps prevent contamination of plasma cell-free nucleic acids with cellular nucleic acids that are released from damaged cells, while also allowing the elimination of processing steps conventionally performed in the art. The present teachings further help to inhibit nuclease activity to protect the integrity of the cell-free plasma nucleic acid. The present teachings may further allow for more rapid analysis of blood samples stored at room temperature for up to about 14 days without compromising the integrity of the cell-free nucleic acids present in the plasma and without contaminating the sample with cellular nucleic acids originating from lysed cells. The present teachings may also make it possible to rapidly analyze samples, while avoid any freezing of plasma of a blood sample and/or contact of the sample with any formaldehyde.

One advantage of the present teachings is the possibility for essentially simultaneous stabilizing of both the nucleated blood cells and cell-free nucleic acids. This helps to prevent cellular genomic nucleic acids (e.g., maternal cellular genomic nucleic acids) from being released into plasma, and further diluting the fetal nucleic acids (and associated biomarkers) of interest, while also maintaining the structural integrity of the fetal nucleic acids. An additional possible advantage of the present teachings lies in its ability to maintain relative amounts of fetal nucleic acids, to afford sufficient analysis. The teachings of the present teachings also contemplate the possibility to arrest the degradation of the fetal nucleic acids post-blood draw.

SUMMARY

The present teachings relate generally to a screening method for the identification of a characteristic of a target nucleic acid in a whole blood sample. The method includes a step of positioning a composition comprising whole blood and at least one preservative agent within a centrifuge. A step of centrifugating the composition at a speed of least about 1000 g for at least about 5 minutes to isolate a plasma that includes at least one target nucleic acid for further analysis is performed. There is also a step of analyzing the at least one target nucleic acid to identify a characteristic about the at least one target nucleic acid. The centrifugating step may be performed at a speed that does not exceed about 10,000 g, about 7500 g, about 4500 g, or even about 2500 g, for more than about 3 minutes, about 2 minutes or even about 1 minute. The centrifugating step may be performed at a speed of at least about 500 g, or even about 1500 g.

The preservative agent may be selected from the group consisting of: diazolidinyl urea, imidazolidinyl urea, dimethoylol-5,5dimethylhydantoin, dimethylol urea, 2-bromo-2.-nitropropane-1,3-diol, oxazolidines, sodium hydroxymethyl glycinate, 5-hydroxymethoxymethyl-1-1aza-3,7-dioxabicyclo [3.3.0]octane, 5-hydroxymethyl-1-1aza-3,7dioxabicyclo[3.3.0]octane, 5-hydroxypoly[methyleneoxy]methyl-1-1aza-3, 7dioxabicyclo[3.3.0]octane, quaternary adamantine and any combination thereof. For example, the preservative agent may be diazolidinyl urea, imidazolidinyl urea, or a combination thereof. The concentration of the preservative agent prior to the centrifugating step may be between about 1% and about 30%. For example, the concentration of the preservative agent prior to the centrifugating step may be between about 4% and about 10%. The concentration of the preservative agent prior to the centrifugating step may be a concentration at which cross-linking of nucleic acids and proteins is observed, as indicated by agarose gel electrophoresis. The concentration of the preservative agent may be less than about 2% of the blood sample. The composition may further include one or more other nonaqueous ingredients selected from the group consisting of glycine, lysine, ethylene diamine, arginine, urea, adinine, guanine, cytosine, thymine, spermidine, ethylenediaminetetraacetic acid (EDTA), aurintricarboxylic acid (ATA), glyceraldehyde, sodium fluoride or combinations thereof. In such instance, the concentration of the preservative agent to the total volume of the one or more other nonaqueous ingredients may range from about 10:1 to about 1:10. The total time of all centrifugation may be below about 18 minutes, about 16 minutes, or even about 12 minutes.

Other features of the teachings include that the method may be free of any centrifugating at two speeds that differ by a factor of at least about 5:1 (e.g., 7:1 or about 10:1). The method may be such that (i) either or both of the centrifugating or analyzing steps occurs within 14 days after the blood sample is drawn, (ii) either or both of the centrifugating or analyzing steps occurs without freezing the blood sample (e.g. to a temperature colder than about −30° C. (more preferably colder than about −70° C.)); or both (i) and (ii). The method may include a step of providing the composition in a blood collection tube into which the whole blood was directly drawn from a subject and within which the preservative agent was present at the time of the blood draw. The method may be free of any second centrifugating step.

Also within the teachings is a composition including the plasma, the preservative agent, and any other ingredient, which is produced by the method of the present teachings.

As the teachings will illustrate, there is contemplated herein a non-invasive screening method for the identification of characteristics of one or more nucleic acid (e.g., without limitation, fetal cell free DNA and/or RNA, and/or nucleic acids (e.g., DNA) of circulating tumor matter, mRNA, or other nucleic acid) derivable form a whole blood sample, and particularly from separated plasma of a whole blood sample. The method may be regarded generally as having a primarily single centrifugation test protocol for obtaining a plasma containing a ready-for-testing amount of at least one target nucleic acid. The method may be regarded generally as having a centrifugation test protocol for obtaining a plasma containing a ready-for-testing amount of at least one target nucleic acid that can be completed in an amount of centrifugation time of less than about 20 minutes. The method may be regarded generally as having a centrifugation test protocol for obtaining a plasma containing a ready-for-testing amount of at least one target nucleic acid that can be completed in an amount of time less than about 15 minutes. The method may be regarded generally as a having a centrifugation test protocol for obtaining a plasma containing a ready-for-testing amount of at least one target nucleic acid that can be completed in the absence of any centrifugation at a speed in excess of about 2500 g. The method may be regarded generally as having a centrifugation test protocol for obtaining a plasma containing a ready-for-testing amount of at least one target nucleic acid that can be completed so that there is a substantially complete absence (e.g., less than about 0.5 percent by weight of the resulting separated plasma) of any contamination from cellular or other components of the whole blood sample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative chart depicting the results of blood plasma cfDNA isolation of post-draw blood samples using EDTA blood collection tubes with a double spin protocol and single spin protocols.

FIG. 2 is an illustrative chart depicting the results of blood plasma cfDNA isolation of post-draw blood samples stored at room temperature using cell-free nucleic acid blood collection tubes with a double spin protocol and a single spin protocol.

FIG. 3 is an illustrative chart depicting the results of blood plasma cfDNA isolation of post-draw blood samples shaken for selected time intervals using cell-free nucleic acid blood collection tubes with a double spin protocol and a single spin protocol.

DETAILED DESCRIPTION

The explanations and illustrations presented herein are intended to acquaint others skilled in the art with the teachings, its principles, and its practical application. Those skilled in the art may adapt and apply the teachings in its numerous forms, as may be best suited to the requirements of a particular use. Accordingly, the specific embodiments of the present teachings as set forth are not intended as being exhaustive or limiting of the teachings. The scope of the teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. Other combinations are also possible as will be gleaned from the following claims, which are also hereby incorporated by reference into this written description.

This application claims the benefit of the filing date of U.S. Provisional Application No. 62/258,404, filed Nov. 20, 2015, the entirety of the contents of that application being hereby incorporated by reference for all purposes.

In general, the teachings herein contemplate a screening method for the identification of a characteristic of a target nucleic acid in a whole blood sample, including positioning a composition comprising whole blood and at least one preservative agent within a centrifuge, centrifugating the composition to isolate a plasma that includes at least one target nucleic acid for further analysis and analyzing the at least one target nucleic acid to identify a characteristic about the at least one target nucleic acid. The method may be free of any second centrifugating step. The nucleic acid may be DNA or RNA or any combination thereof. The teachings also contemplate a composition including the plasma, the preservative agent, and any other ingredient, which is produced by the method.

The method includes contacting a blood sample with a preservative agent. The preservative agent may be selected from the group consisting of diazolidinyl urea, imidazolidinyl urea, dimethoylol-5,5dimethylhydantoin, dimethylol urea, 2-bromo-2.-nitropropane-1,3-diol, oxazolidines, sodium hydroxymethyl glycinate, 5-hydroxymethoxymethyl-1-1aza-3,7-dioxabicyclo[3.3.0]octane, 5-hydroxymethyl-1-1aza-3,7dioxabicyclo[3.3.0]octane, 5-hydroxypoly[methyleneoxy]methyl-1-1aza-3, 7dioxabicyclo [3.3.0]octane, quaternary adamantine, 2-aminoacetic acid or any combination thereof. Preferred ingredients are selected from the group consisting of diazolidinyl urea (DU), imidazolidinyl urea (IDU), and any combination thereof. The preservative agent may be part of a protective agent composition.

The protective agent may consist essentially of the active ingredient. It may be at least about 10%, 50%, or even 80% by volume of the protective agent. For instance, the concentration of active ingredient within the protective agent used may be generally about 10% to about 80%. The concentration of active ingredient within the protective agent may be at least about 25% or even 50%. For example, the protective agent may comprise about 0.05 to about 0.4 grams of a formaldehyde releaser preservation agent (e.g., IDU, DU, or combinations thereof) per 0.2 ml of the total protective agent.

As used throughout the present teachings, the protective agent composition preferably is substantially non-toxic. For example, the methods herein (and compositions used herein) may be free of separately adding and/or handling of any materially significant concentration (e.g., less than about 1% by weight, more preferably less than about 2000 parts per million, more preferably less than about 1000 parts per million, and still more preferably less than about 500 parts per million) of formaldehyde and/or paraformaldehyde prior to any contact with a blood product sample.

The protective agent may include a nuclease inhibitor in a suitable amount to prevent DNase and RNase activity from further decreasing (e.g. by at least about 10% by weight, and more preferably at least about 50% by weight) the quality and amount of nucleic acids recoverable from the blood sample as compared with a sample that does not include a nuclease inhibitor. Nuclease inhibitors that may be used include, but are not limited to diethyl pyrocarbonate, ethanol, aurintricarboxylic acid (ATA), formamide, vanadyl-ribonucleoside complexes, macaloid, ethylenediamine tetraacetic acid (EDTA), proteinase K, heparin, hydroxylamine-oxygen-cupric ion, bentonite, ammonium sulfate, dithiothreitol (DTT), beta-mercaptoethanol, cysteine, dithioerythritol, tris (2-carboxyethyl) phosphene hydrochloride, or a divalent cation such as Mg⁺², Mn⁺², Zn⁺², Fe⁺², Ca⁺², Cu⁺² or any combination thereof. Further, the protective agent may be substantially free of guanidinium salts, sodium dodecyl sulfate (SDS), or any combination thereof.

The protective agent may comprise an active agent in solution. Suitable solvents include water, saline, dimethylsulfoxide, alcohol and mixtures thereof. The protective agent may comprise diazolidinyl urea (DU) and/or imidazolidinyl urea (IDU) in a buffered salt solution. The protective agent may further comprise EDTA and 2-aminoacetic acid. Alternatively, the protective agent may contain only a fixative (e.g., an active ingredient) and may be free of any additional additives.

The amount of any active ingredient within the protective agent may generally be about 10% to about 90% by weight. The active ingredient or fixative may comprise about 70% to about 90% by weight of the protective agent. The protective agent may further contain an anticoagulant such as about 5% to about 20% by weight EDTA. The protective agent may contain about 10% by weight EDTA. The protective agent may include from about 1% to about 40% by weight of nuclease inhibitor.

The amount of active ingredient or fixative (e.g. the formaldehyde releaser) relative to the amount of EDTA may be about 1 to about 10 parts (more preferably about 2 to about 8 parts) by weight of fixative to about 1 part by weight EDTA. The amount of protective agent within a tube prior to blood draw may be about 0.05 to about 1.0 ml and more preferably about 0.1 to about 0.3 ml.

The combination of an active ingredient or fixative (e.g. the formaldehyde releaser) and anticoagulant within the protective agent results in improved ability to maintain the amount and quality of a target nucleic acid within a blood sample. These results are believed unexpected and superior to results obtained by the use of only the fixative or only the anticoagulant. Therefore it is believed that a synergistic effect may occur when both a fixative and anticoagulant are combined. The compositions disclosed herein specifically envision the possibility to include the combination of a formaldehyde releaser and an anticoagulant.

The protective agent may be located within a specialized device, wherein the protective agent is already present in the device prior to addition of the blood sample, such as that disclosed in U.S. Patent Publication No. 2004/0137417, incorporated by reference herein. The device may be an evacuated collection container, usually a tube.

The tube as described above may preferably include an anticoagulant agent and an active ingredient such as a fixative agent including but not limited to those active ingredients disclosed herein. The tube may also may further include a nuclease inhibitor. Preferably, the compounds included in the tube are in an amount sufficient to preserve cell morphology and prevent cell degradation while also preventing deleterious DNase and RNase activity within the cell-free nucleic acids. However, the amount of protective agent may also be sufficiently small so that any consequential dilution of the sample is substantially avoided, and cell-free nucleic acids in the sample are not materially diluted. A blood sample may be fixed simultaneously as it is drawn into the specialized tube.

As discussed herein, contacting a blood or plasma sample with the protective agent allows the sample to be stored for a period of time prior to isolating and testing the nucleic acids. More preferably, a blood or plasma sample may be drawn at one location (e.g., a health care facility), contacted with the protective agent, and later transported to a different remote location (e.g., a laboratory, such as one that is separately housed at a distance of at least about 1 km, 2 km, 3 km, or further away from the draw site) for the nucleic acid isolation and testing process. For example, fetal nucleic acids may be isolated from the maternal blood or plasma sample and tested for various fetal characteristics (including but not limited to chromosomal abnormalities) at the remote location and the resulting diagnostic information may then be reported to the site of the original blood draw.

At any time after the initial contact of the blood or plasma sample with the protective agent, the sample can be treated to isolate the nucleic acids located within the blood sample. The nucleic acids may be isolated using any isolation method including those methods disclosed in U.S. Patent Publication No. 2009/0081678, incorporated by reference herein.

The methods herein thus further contemplate a step of nucleic acid testing. Testing of the nucleic acids can be performed using any nucleic acid testing method including, but not limited to polymerase chain reaction (PCR), reverse transcription polymerase chain reaction (RT-PCR), quantitative real time polymerase chain reaction (Q-PCR), gel electrophoresis, capillary electrophoresis, mass spectrometry, fluorescence detection, ultraviolet spectrometry, DNA hybridization, allele specific polymerase chain reaction, polymerase cycling assembly (PCA), asymmetric polymerase chain reaction, linear after the exponential polymerase chain reaction (LATE-PCR), helicase-dependent amplification (HDA), hot-start polymerase chain reaction, intersequence-specific polymerase chain reaction (ISSR), inverse polymerase chain reaction, ligation mediated polymerase chain reaction, methylation specific polymerase chain reaction (MSP), multiplex polymerase chain reaction, nested polymerase chain reaction, solid phase polymerase chain reaction, or any combination thereof.

One aspect of the teachings herein contemplates a method for isolating and testing cell-free fetal DNA from maternal plasma. The method may be performed on a single sample or on a multitude of samples (e.g., in a multi-well plate). The method may include contacting the maternal plasma sample with a protective agent. The protective agent may include a fixative as previously discussed so that the maternal cells remain intact throughout the blood draw and DNA isolation process. The protective agent may further include a DNase inhibitor to maintain the structural integrity of the fetal DNA. After contacting the maternal plasma sample with the protective agent, the sample may be centrifuged to separate the plasma and the supernatant is discarded. By contacting a maternal blood sample with the protective agent, the blood sample does not necessarily require secondary centrifugation or immediate processing and may be stored for a prolonged period, such as up to about 14 days or longer at room temperature. Thus the teachings herein contemplate one or more steps of storing and/or otherwise waiting a relatively lengthy period from the time of blood draw and/or contacting until the time of screening, testing or other analysis.

Once, the sample is processed, an appropriate concentration of an agent for inducing precipitation (e.g., a composition of salt and/or alcohol) may be added to precipitate the fetal DNA containing material. An organic or other compound such as a phenol derivative or the like may be added to remove any remaining protein contaminants. Any protein contaminants that still remain may be removed by adding additional amounts of an organic or other compound such as a phenol derivative or the like. After centrifugation, ethanol may be added and the sample centrifuged again. Any remaining liquid may be removed from the sample so only the fetal DNA will remain. The finished product of isolated fetal DNA may then be contacted with a buffer.

One or more steps of incubation may be performed. Incubation may occur on ice or at any temperature between −30° C. and 70° C. For example, a sample may be incubated at about −20° C. A sample may also be stored at room temperature and thus substantially free of freezing upon blood draw. The sample may be substantially free of freezing at any time between blood draw and any downstream processing (e.g., isolation and/or analysis).

Centrifugation may be performed at a suitable rate. For example, centrifugation may be done at about 500 to about 20,000 rpm. Centrifugation may occur at about 1,000 to 16,000 rpm. Centrifugation may be performed at about room temperature or cooler. For example, it may be performed at about 1-20° C., or still more specifically at about 4-9° C.

The protective agent of the present teachings may be placed within a tube so that the tube contains about 0.20 ml of the protective agent. The tube containing the protective agent may receive about 10 ml of patient blood. The patient blood may be drawn directly into the tube containing the protective agent.

The protective agent may include a preserving agent and an anticoagulant. The preserving agent may be imidazolidinyl urea or diazolidinyl urea. The imidazolidinyl urea may be present in an amount of about 300 g/l to about 700 g/l of the protective agent. The imidazolidinyl urea may be about 0.05% to about 3% of the protective agent. The diazolidinyl urea may be present in an amount of about 50 g/l to about 400 g/l of the protective agent. The diazolidinyl urea may be about 0.05% to about 2.5% of the protective agent. The anticoagulant may be selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), salts of EDTA, heparin, citrate, oxalate, and any combination thereof. The anticoagulant may be K3EDTA. The K3EDTA may be present in an amount of about 20 g/l to about 150 g/l of the protective agent. The K3EDTA may be present in an amount of about 50 g/l to about 100 g/l of the protective agent. The protective agent may include a preserving agent, an anticoagulant and glycine. The glycine may be present in an amount of about 10 g/l to about 150 g/l of the protective agent. The glycine may be present in an amount of about 35 g/l to about 100 g/l of the protective agent. The protective agent may include a preserving agent, an anticoagulant and ingredients selected from the group consisting of glyceraldehyde, sodium fluoride (NaF), aurintricarboxylic acid (ATA), or combinations thereof. The glyceraldehyde may be present in amount of about 10 g/l to about 150 g/l of the protective agent. The glyceraldehyde may be present in amount of about 35 g/l to about 100 g/l of the protective agent. The sodium fluoride (NaF) may be present in an amount of about 0.1 g/l to about 30 g/l of the protective agent. The sodium fluoride (NaF) may be present in an amount of about 0.05 g/l to about 10 g/l of the protective agent. The aurintricarboxylic acid (ATA) may be present in an amount of about 1 g/l to about 40 g/l of the protective agent. The aurintricarboxylic acid (ATA) may be present in an amount of about 5 g/l to about 20 g/l of the protective agent.

Double spin protocols are commonly used to separate blood plasma for cfDNA isolation. Double spin protocols start with a low speed spin to minimize cell lysis during the plasma isolation step, potentially caused by centrifugation spin speed, followed by high speed centrifugation to remove the low quantity of residual cells remaining. The two spin process is a lengthy/time consuming step in the specimen processing procedure. Table 1 depicts a comparison of two different double spin protocols and a single spin protocol.

TABLE 1 Double Spin Double Spin Single Spin Protocol A Protocol B Protocol 300 g for 20 minutes 1600 g for 15 minutes 1600 g for 15 minutes Transfer plasma Transfer plasma Collect cell-free to a new to a new plasma for DNA tube (20 samples) tube (20 samples) isolation 15 minutes 15 minutes 5,000 g for 16,000 g for 10 minutes 10 minutes Collect cell-free Collect cell-free plasma for plasma for DNA isolation DNA isolation Estimated Total Time: Estimated Total Time: Estimated Total Time: 45 minutes 40 minutes 15 minutes

In verifying the protective capabilities of the compositions disclosed herein, standard EDTA blood collection tubes are thus compared against cell free nucleic acid blood collection tubes containing the protective agent of the present teachings, which thus contains a composition that stabilizes nucleated blood cells and inhibits plasma nucleases. The results of a double spin protocol and single spin protocols for blood plasma cfDNA isolation of blood samples collected in the respective tubes are also compared.

Example 1

Blood was collected into EDTA blood collection tubes and divided into 3 groups for a double spin process of 300×g for 20 min followed by 5000×g for 10 min, a single spin process of 1600×g for 15 minutes, and a single spin process of 5000×g for 15 minutes, respectively. Samples were stored at room temperature and cfDNA was isolated on day 0 and day 3. Total plasma cfDNA was assayed by droplet digital PCR. The comparison of the cell-free DNA concentrations in plasma revealed a statistically significant difference between the samples. FIG. 1 illustrates the results of blood plasma cfDNA isolation of post-draw blood samples using EDTA blood collection tubes and double spin protocols and a single spin protocol. The findings indicate that the double spin protocol is preferred over a single spin protocol with blood collected in EDTA blood collection tubes for isolation of plasma cfDNA.

Example 2

Blood was collected into 10 mL cell-free nucleic acid blood collection tubes of the present teachings and divided into 2 groups for the single spin process (i.e. 1600×g for 15 min) and the double spin process (i.e. 300×g for 20 min followed by 5000×g for 10 min), respectively. Samples were stored at room temperature and cfDNA was isolated on day 0, 7, and 14. Total plasma cfDNA was assayed by droplet digital PCR. The comparison of the cell-free DNA concentrations in plasma revealed no statistically significant difference between “paired samples” (i.e. single spin vs. double spin) in the storage study. FIG. 2 illustrates the results of blood plasma cfDNA isolation of post-draw blood samples stored at room temperature using cell-free nucleic acid blood collection tubes and a double spin protocol and a single spin protocol. The findings indicate that the single spin protocol is compatible with the plasma separation procedure from blood collected in cell-free nucleic acid blood collection tubes for isolation of plasma cfDNA. The results for samples tested one or two weeks after the blood draw are not expected to vary by more than +/−10%.

Example 3

Blood was collected into 10 mL cell-free nucleic acid collection tubes of the present teachings and divided into 2 groups for the single spin process (i.e. 1600×g for 15 min) and the double spin process (i.e. 300×g for 20 min followed by 5000×g for 10 min), respectively. The single spin protocol was compared with the double spin protocol in a shaking study to simulate conditions that may occur during sample shipping. Samples were shaken for time intervals of 0 hours, 3 hours, 6 hours and 24 hours. Total plasma cfDNA was assayed by droplet digital PCR. The comparison of the cell-free DNA concentrations in plasma revealed no statistically significant difference between “paired samples” (i.e. single spin vs. double spin) at each shaking time point (n=5 donors). FIG. 3 illustrates the results of blood plasma cfDNA isolation of post-draw blood samples shaken for selected time intervals using cell-free nucleic acid blood collection tubes and a double spin protocol and a single spin protocol. The findings indicate that the single spin protocol is compatible with the plasma separation procedure from blood collected in cell-free nucleic acid blood collection tubes for isolation of plasma cfDNA.

The examples and testing results discussed above demonstrate the merits of a “single spin protocol” for plasma DNA isolation from blood stored in cell-free nucleic acid blood collection tubes of the present teachings without introducing cellular DNA contamination. The double spin protocol was developed for blood drawn into regular tubes, e.g. EDTA tubes. The findings indicate that a double spin protocol is preferred over a single spin protocol with blood collected in EDTA blood collection tubes. However, a single spin protocol is compatible for use with blood samples collected and “stabilized” into cell-free nucleic blood collection tubes of the present teachings. The single spin protocol allows for plasma DNA isolation from blood stored in cell-free nucleic blood collection tubes without introducing cellular DNA contamination.

It will be appreciated that concentrates or dilutions of the amounts recited herein may be employed. In general, the relative proportions of the ingredients recited will remain the same. Thus, by way of example, if the teachings call for 30 parts by weight of a Component A, and 10 parts by weight of a Component B, the skilled artisan will recognize that such teachings also constitute a teaching of the use of Component A and Component B in a relative ratio of 3:1. Teachings of concentrations in the examples may be varied within about 25% (or higher) of the stated values and similar results are expected.

It will be appreciated that the above is by way of illustration only. Other ingredients may be employed in any of the compositions disclosed herein, as desired, to achieve the desired resulting characteristics. Examples of other ingredients that may be employed include antibiotics, anesthetics, antihistamines, preservatives, surfactants, antioxidants, unconjugated bile acids, mold inhibitors, nucleic acids, pH adjusters, osmolarity adjusters, polymers (e.g., PVP, PEG, cyclodextrin) or any combination thereof.

It should be recognized that in the present teachings, unless otherwise stated, reference in a teaching to the generic form of “nucleic acid” contemplates not only the genus of nucleic acids, but also individual species of nucleic acid (such as fetal DNA, fetal RNA, DNA, RNA, mRNA, tumor DNA, tumor RNA, or otherwise) even if such species is not referenced in the passage at hand.

As used herein, unless otherwise stated, the teachings envision that any member of a genus (list) may be excluded from the genus; and/or any member of a Markush grouping may be excluded from the grouping.

Unless otherwise stated, any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component, a property, or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that intermediate range values such as (for example, 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc.) are within the teachings of this specification. Likewise, individual intermediate values are also within the present teachings. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. As can be seen, the teaching of amounts expressed as “parts by weight” herein also contemplates the same ranges expressed in terms of percent by weight. Thus, an expression in the Detailed Description of the Teachings of a range in terms of at ‘“χ’ parts by weight of the resulting composition” also contemplates a teaching of ranges of same recited amount of “x” in percent by weight of the resulting composition.”

Unless otherwise stated, all ranges include both endpoints and all numbers between the endpoints. The use of “about” or “approximately” in connection with a range applies to both ends of the range. Thus, “about 20 to 30” is intended to cover “about 20 to about 30”, inclusive of at least the specified endpoints. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. The term “consisting essentially of to describe a combination shall include the elements, ingredients, components or steps identified, and such other elements ingredients, components or steps that do not materially affect the basic and novel characteristics of the combination. The use of the terms “comprising” or “including” to describe combinations of elements, ingredients, components or steps herein also contemplates embodiments that consist essentially of (namely, the presence of any additional elements, ingredients, components or steps, does not materially affect the properties and/or benefits derived from the teachings; for example, the inclusion of a second very brief centrifugation step, such as for less than about 20%, 15%, 10% of the time of the primary centrifugation step described herein) or even consist of the elements, ingredients, components or steps.

Plural elements, ingredients, components or steps can be provided by a single integrated element, ingredient, component or step. Alternatively, a single integrated element, ingredient, component or step might be divided into separate plural elements, ingredients, components or steps. The disclosure of “a” or “one” to describe an element, ingredient, component or step is not intended to foreclose additional elements, ingredients, components or steps. All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements published and copyrighted by CRC Press, Inc., 1989. Any reference to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.

It is understood that the above description is intended to be illustrative and not restrictive. Many embodiments as well as many applications besides the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. The omission in the following claims of any aspect of subject matter that is disclosed herein is not a disclaimer of such subject matter, nor should it be regarded that the inventors did not consider such subject matter to be part of the disclosed inventive subject matter.

The explanations and illustrations presented herein are intended to acquaint others skilled in the art with the teachings, its principles, and its practical application. Those skilled in the art may adapt and apply the teachings in its numerous forms, as may be best suited to the requirements of a particular use. Accordingly, the specific embodiments of the present teachings as set forth are not intended as being exhaustive or limiting of the teachings. The scope of the teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. Other combinations are also possible as will be gleaned from the following claims, which are also hereby incorporated by reference into this written description. 

1: A screening method for the identification of a characteristic of a target nucleic acid in a whole blood sample, comprising the steps of: a. positioning a composition comprising whole blood (bio sample?) and at least one preservative agent within a centrifuge; b. centrifugating the composition at a speed of least about 1000 g for at least about 5 minutes to isolate a plasma that includes at least one target nucleic acid for further analysis; c. analyzing the at least one target nucleic acid to identify a characteristic about the at least one target nucleic acid, wherein the centrifugating step is performed at a speed that does not exceed 7500 g for more than 1 minute. 2: The method of claim 1, wherein the preservative agent is selected from the group consisting of: diazolidinyl urea, imidazolidinyl urea, dimethoylol-5,5dimethylhydantoin, dimethylol urea, 2-bromo-2.-nitropropane-1,3-diol, oxazolidines, sodium hydroxymethyl glycinate, 5-hydroxymethoxymethyl-1-1aza-3,7-dioxabicyclo [3.3.0]octane, 5-hydroxymethyl-1-1aza-3,7dioxabicyclo[3.3.0]octane, 5-hydroxypoly[methyleneoxy]methyl-1-1aza-3, 7dioxabicyclo[3.3.0]octane, quaternary adamantine and any combination thereof. 3: The method of claim 2, wherein the concentration of the preservative agent prior to the centrifugating step is between about 1% and about 30% 4: The method of claim 1, wherein the concentration of the preservative agent prior to the centrifugating step is between about 4% and about 10%. 5: The method of claim 1, wherein the concentration of the preservative agent prior to the centrifugating step is a concentration at which cross-linking of nucleic acids and proteins is observed, as indicated by agarose gel electrophoresis. 6: The method of claim 2, wherein the concentration of the preservative agent is less than about 2% of the blood sample. 7: The method of claim 1, wherein the composition further includes one or more other nonaqueous ingredients selected from the group consisting of glycine, lysine, ethylene diamine, arginine, urea, adinine, guanine, cytosine, thymine, spermidine, ethylenediaminetetraacetic acid (EDTA), aurintricarboxylic acid (ATA), glyceraldehyde, sodium fluoride or combinations thereof. 8: The method of claim 7, wherein the ratio (by volume) of the concentration of the preservative agent to the total volume of the one or more other nonaqueous ingredients ranges from about 10:1 to about 1:10. 9: The method of claim 1, wherein the centrifugating step consists of a single step of centrifugating the composition at a speed below about 4500 g. 10: The method of claim 1, wherein the centrifugating step consists of a single step of centrifugating the composition at a speed below about 2500 g. 11: The method of claim 1, wherein the centrifugating step consists of a single step of centrifugating the composition at a speed of at least about 500 g. 12: The method of claim 1, wherein the centrifugating step consists of a single step of centrifugating the composition at a speed of at least about 1500 g. 13: The method of claim 1, wherein the total time of all centrifugation is below about 18 minutes.
 14. The method of claim 1, wherein the method is free of any centrifugating at two speeds that differ by a factor of at least about 5:1 (e.g., 7:1 or about 10:1).
 15. The method of claim 14, wherein (i) either or both of the centrifugating or analyzing steps occurs within 14 days after the blood sample is drawn, (ii) either or both of the centrifugating or analyzing steps occurs without freezing the blood sample (e.g. to a temperature colder than about −30° C. (more preferably colder than about −70° C.)); or both (i) and (ii).
 16. A composition including the plasma, the preservative agent, which is produced by the method of claim
 1. 17: A screening method for the identification of a characteristic of a target nucleic acid in a biological sample, comprising the steps of: a. collecting a biological sample having at least one first phase dispersed within at least one second phase; b. modifying a characteristic of the first phase or the second phase for increasing the rate of phase separation between the first phase and the second phase during centrifugation of each of a plurality of individual cells within the biological sample c. continuously centrifugating the biological sample at a speed of least about 1000 g for at least about 5 minutes to form an isolated plasma that includes at least one target nucleic acid for further analysis; d. removing at least a portion of the isolated plasma for further analysis; wherein the method is free of any second centrifugating step after the removing step d. 18: The method of claim 17, wherein the characteristic modified is a surface energy characteristic, a surface area characteristic, a size characteristic, a density characteristic, or any combination thereof. 19: The method of claim 17, wherein the density is modified by increasing the density of the plurality of blood cells by at least about 10%. 20: The method of claim 17, wherein the density is modified by decreasing the density of the plurality of blood cells by at least about 10%. 